Situation;
83 944 engine in an '87 924s
currently temp gauge rises slightly and stays there, just a little off stone cold
The temperature gauge sender is different (small button style in '83 block with no "probe" vs. a single spade larger thread sender the 924s gauge wants; with a probe) with different resistance values no doubt.
Possible solutions;
1) drill and tap the block to accept the larger 924s sender
2) swap the gauge in the dash; either the whole temp/fuel/idiot light nacelle or just the temp part, no idea how they hook up or how interchangeable they are.
Thoughts?_________________87 924S project, '83 944 engine,
my son's first car.

If you're not a stickler for originality you could fabricate a piece of tubing with a proper threaded boss welded into it to fit the sender you require for your present gauge which then splices into a coolant hose and there you have it. Easy peasy, and you don't need to mess with the block or the dash...used to do this on the race cars all of the time.
Edit!
Oh I almost forgot since I'm old and we used to use mechanical gauges mostly...you may need to make a provision for a ground wire connection by welding/brazing an electrical spade on your tubing or use some other method of grounding the sender._________________'95 BMW 318i/5 "Pearl"
'86 Porsche 944 Turbo...Parting, Not Much Left!
'87 Porsche 944 NA "Liebchen"
'04 BMW X5 "Moby"